The present invention relates generally to catheters and, in particular, though not exclusively, to double-lumen catheters used for hemodialysis.
Hemodialysis catheters are conventionally large double-lumen catheters. Generally, the lumens must be large enough to support flow rates greater than 250 c c/min through each lumen. A hemodialysis catheter resides within a large vein within the body or within the right atrium of the heart. The end of the catheter placed into a patient""s body is referred to as the distal end of the catheter, while the end connected to a dialysis machine is called the proximal end. Blood is withdrawn out of a vein via an uptake lumen of the catheter and into the dialysis machine. The uptake lumen is also referred to herein as the withdrawal lumen. The dialyzed blood is returned to the body via the return lumen. The uptake lumen has an uptake lumen hole (also referred to as an uptake lumen opening) for withdrawal of blood from the body. The uptake lumen hole is typically disposed at the distal end of the uptake lumen. Similarly, the return lumen has a return lumen hole for return of blood to the body. The return lumen hole is typically disposed at the distal end of the return lumen. The uptake and return lumen holes are generally spatially separated from each other, typically with the uptake lumen hole located proximal to the return lumen. This is usually accomplished by making the uptake lumen shorter than the return lumen. The above configuration of the uptake and return lumen holes minimizes the immediate redialysis of blood just returned to the body.
FIG. 1 is a side view of a first embodiment of double lumen catheters in the prior art. In FIG. 1, catheter 100 includes a proximal end 110, a distal end 120, and a central axis 130. The central axis may also herein be referred to as the longitudinal axis. Catheter 100 also includes an uptake lumen end hole 141 and a return lumen end hole 142. As can be seen in FIG. 1, uptake lumen end hole 141 is located proximally with respect to return lumen end hole 142.
On occasion, prior art catheters, such as that shown in FIG. 1, fail to perform their intended function. The failure modes of these catheters are numerous. One common type of failure is occlusion of the uptake lumen end hole by the adjacent wall of the vein or by the wall of the right atrium. That is, when blood is withdrawn at a rapid rate from the vein via the uptake lumen, the uptake lumen end hole has a propensity to aspirate (or xe2x80x9csuck upxe2x80x9d) against any adjacent structure. This adverse action of the uptake lumen end hole either limits the flow rate of the catheter or occludes blood flow entirely through the catheter.
Some of the available hemodialysis catheters address this problem by designing the uptake lumen to have several side holes. FIG. 2 is a side view of a prior art catheter having such side holes. Catheter 200, in FIG. 2, has a proximal end 210, a distal end 220, and a central axis 230. Catheter 200 also includes uptake lumen side holes 241 in the uptake lumen and return lumen side holes 242 in the return lumen. With this configuration, even if one side hole of the uptake lumen is sucked or aspirated against an adjacent wall, the catheter functions because the other side holes of the uptake lumen are not aspirated against the wall.
However, this design, in which multiple side holes are present to prevent occlusion by adjacent walls, presents a drawback of its own. When any hemodialysis catheter is not in use, both lumens are filled (or xe2x80x9clockedxe2x80x9d) with an anticoagulant solution, typically concentrated heparin sulfate. This solution is intended to prevent blood clots from forming on or within the catheter""s lumens. Such blood clots would occlude the lumens, leading to catheter failure. If the uptake lumen has multiple side holes, the anticoagulant solution leaks away at the catheter tip through these multiple side holes, causing an increased risk of blood clot formation on the catheter""s tip, thus causing subsequent catheter failure.
A hemodialysis catheter whose uptake lumen consists of a single end hole will retain the anticoagulant solution. However, as detailed above, such a prior-art hemodialysis catheter retains a tendency to have its uptake lumen end hole aspirate against an adjacent wall and occlude the uptake lumen.
The intravenous portion of conventional hemodialysis catheters are linear in configuration. The lumens of such catheters run parallel to each other within a single, flexible silicone housing, with the lumens separated by a silicone septum. FIGS. 3a, 3b, and 3c are a first, second, and third embodiments, respectively, of the cross sectional view along each of lines 3xe2x80x943 in FIGS. 1 and 2. The views in FIGS. 3a, 3b, and 3c represent different embodiments for partitioning the uptake and return lumens. In FIGS. 3a, 3b, and 3c, cross sections 301 and 302 represent cross sections of the uptake lumen and return lumen, respectively, in the three different embodiments of the cross sections of the catheter. FIGS. 3a, 3b, and 3c also represent three different embodiments of the view along the central axis from the distal end to the proximal end (as well as the view along the central axis from the proximal end to the distal end) in the catheters of FIGS. 1 and 2.
Discussion of prior art catheters, such as those described above, can be found in U.S. Pat. No. 5,209,723, U.S. Pat. No. 5,947,953, and U.S. Pat. No. 6,001,079, which are incorporated by reference herein.
Accordingly, there is a need for a catheter that addresses the above disadvantages of prior art catheters.
The present invention encompasses a catheter. In one embodiment, the catheter includes: a shaft segment, the shaft segment including a proximal end of the catheter and a shaft segment central axis, the shaft segment further including a shaft S segment uptake lumen and a shaft segment return lumen; a distal end segment coupled to the shaft segment, the distal end segment including a distal end of the catheter and a distal end segment central axis, the distal end segment further including a distal end segment uptake lumen and a distal end segment return lumen, where the distal end segment uptake and return lumens are coupled to the shaft segment uptake and return lumens, respectively; where the distal end segment central axis forms a non-zero angle with the shaft segment central axis when the catheter is in its unstressed configuration.
In a second embodiment, the catheter includes: a shaft segment, the shaft segment including a proximal end of the catheter and a shaft segment central axis; a distal end segment coupled to the shaft segment, the distal end segment including a distal end of the catheter and a distal end segment central axis; where the distal end segment central axis is parallel to the shaft segment central axis when the catheter is in its unstressed configuration, further where the distal end segment includes a return lumen and an uptake lumen having a return lumen distal end and an uptake lumen distal end, respectively, further where the uptake lumen distal end is terminated by a closed surface, further where the uptake lumen distal segment includes only one side hole.
In a third embodiment, the catheter includes: an uptake lumen including an uptake lumen shaft segment and an uptake lumen distal segment with an uptake lumen distal end; a return lumen including a return lumen shaft segment and a return lumen distal segment with a return lumen distal end; where the uptake lumen shaft segment is substantially parallel to the return lumen shaft segment, further where at least a portion of the return lumen distal segment is helically coiled around the uptake lumen distal end.